“We see that 2018 might not be quite so happy for Opec producers, ” the Paris-based organization said in its latest monthly report Thursday.The IEA said that there were signs that the rise in U.S. crude oil supply was likely to continue into 2018 and upset rivals who are cutting back.Major oil producing group OPEC and ten non-OPEC producers led by Russia continue to cut production in order to boost global oil prices and rebalance markets put out of kilter in 2014 by a glut in supply and lackluster demand.One of the main beneficiaries of these cuts is the producers’ major competitor, U.S. shale oil. U.S. oil producers are staging a dramatic comeback amid a recovering oil price that has allowed many of them to restart operations.